A hybrid machine, roughly speaking, includes an engine, a generator with the engine as a drive source, an electric motor, and a secondary battery for storing electromotive force of the electric motor generated by reverse driving of the electric motor by an external load, in which the electric motor receives electric power from the generator and the secondary battery so as to be driven. Hybridization aims at saving of energy and a reduction in pollution, and in recent years, it has been put to practical use in an ordinary vehicle and achieves favorable results. The saving of energy results from regeneration of electromotive force based on the reverse driving of the electric motor generated when a vehicle is braked and goes downhill as driving electric power for the electric motor, and a reduction in the fuel consumption of the engine owing to this regeneration. Meanwhile, the reduction in pollution results from the reduction in the fuel consumption of the engine, that is, a reduction in exhaust gas.
Incidentally, energy recovery of storing the electromotive force based on the reverse driving of the electric motor in the second battery in the ordinary vehicle can be expected in city traveling accompanied by frequent braking, but it is difficult to expect the energy recovery in expressway traveling accompanied by infrequent braking. Namely, according to this hybrid ordinary vehicle, the energy recovery cannot be performed constantly.
However, in construction equipment such as a hydraulic shovel or a wheel loader, a mine machinery, mechanical handling equipment such as a folklift, or the like provided with a hydraulic drive device which constantly performs repetitive operation, the hydraulic drive device has hydraulic cylinders which can be repeatedly extended/contracted not only against external loads but also by the external loads. Further, the machine such as a hydraulic shovel having a rotation mechanism has rotation motors which repeat normal/reverse rotations and receive rotation inertial force as an external load when being braked. Namely, according to these machines, energy recovery can be performed constantly from the hydraulic cylinders and/or the rotation motors.
Accordingly, if such a machine with the hydraulic drive device is hybridized, it can achieve the saving of energy and reduction in pollution more constantly at least than the hybrid ordinary vehicle, whereby the hybridization of such a machine with the hydraulic drive device is desired.